//! Loading / parsing

use crate::{
    COLOR_SECTIONS, Emphasis, Rgb, STEP_FLOOR, SemanticTokens, ThemeColors, ThemeMeta,
    find_theme_path, resolve, tonal, wcag_contrast,
};
use serde::Serialize;
use std::collections::HashMap;
use std::path::{Path, PathBuf};

// Names this module's prose links to, resolved for rustdoc.
#[allow(unused_imports)]
use crate::ansi_intent;

/// Validate a theme ID contains only safe characters (alphanumeric, hyphens, underscores).
pub fn validate_theme_id(id: &str) -> Result<(), String> {
    if !id
        .chars()
        .all(|c| c.is_alphanumeric() || c == '-' || c == '_')
    {
        return Err(format!("Invalid theme ID: {id}"));
    }
    Ok(())
}

/// Parse the `[meta]` section into `ThemeMeta`.
///
/// Falls back to the file ID as the name and `"dark"` as the variant.
pub fn parse_meta(id: &str, table: &toml::Table, is_custom: bool) -> ThemeMeta {
    let meta = table.get("meta").and_then(|m| m.as_table());
    let name = meta
        .and_then(|m| m.get("name"))
        .and_then(|v| v.as_str())
        .unwrap_or(id)
        .to_string();
    let variant = meta
        .and_then(|m| m.get("variant"))
        .and_then(|v| v.as_str())
        .unwrap_or("dark")
        .to_string();

    ThemeMeta {
        id: id.to_string(),
        name,
        variant,
        is_custom,
    }
}

/// Extract the intent color sections into a flat `HashMap` with dotted keys
/// like `"surface.page"`, `"status.danger"`, `"category.one"`.
///
/// The tonal steps of `content.primary` are filled in here rather than read, by
/// [`derive_tonal_steps`]. Anything a theme authored under those keys is
/// replaced.
pub fn extract_colors(table: &toml::Table) -> HashMap<String, String> {
    let mut colors = HashMap::new();
    for section in COLOR_SECTIONS {
        if let Some(sect) = table.get(*section).and_then(|s| s.as_table()) {
            for (key, val) in sect {
                if let Some(color) = val.as_str() {
                    colors.insert(format!("{section}.{key}"), color.to_string());
                }
            }
        }
    }
    derive_tonal_steps(&mut colors);
    colors
}

/// Fill in the tonal steps of `content.primary`, overwriting whatever the theme
/// authored under those keys.
///
/// # Why they are not authored
///
/// `content.secondary` and `content.muted` are not independent colours. They are
/// the ink, one step and two steps back, and a theme that names them separately
/// is stating three times something it stated once — which is how three of the
/// bundled themes came to author a `secondary` *lighter* than their own
/// `primary` (nord, solarized-dark) or identical to it (dracula), inverting the
/// emphasis ramp the whole vocabulary rests on. Deriving them makes
/// `content` > `content-secondary` > `content-muted` true by construction in
/// every theme, including one a user writes.
///
/// Applied at load rather than in [`resolve`] so that there is one answer: the
/// resolved token layer, the ANSI table ([`ansi_intent`] reads authored keys),
/// and every consumer holding a [`ThemeColors`] all see the same value. A
/// derivation visible from only one of those is how a terminal and a webview
/// come to disagree about what muted means.
///
/// Both keys need `content.primary` and `surface.page` to exist and parse. When
/// either is missing the step is skipped and anything authored is left where it
/// is, mirroring the skip-missing behaviour of the rest of the crate — a
/// half-written theme keeps whatever it has rather than losing it.
///
/// # The ratio is a starting point, not the answer
///
/// Each step is pushed further toward the page until it clears [`STEP_FLOOR`]
/// against the ink, so what the theme gets is a step that can be seen rather
/// than a step of the agreed size. The two are the same number in every bundled
/// theme but the two with a pure-black ink, where the ratio has no range to
/// travel in and the nominal step lands 3/255 from where it started.
pub fn derive_tonal_steps<S: std::hash::BuildHasher>(colors: &mut HashMap<String, String, S>) {
    let ink = colors.get("content.primary").and_then(|v| Rgb::from_hex(v));
    let page = colors.get("surface.page").and_then(|v| Rgb::from_hex(v));
    let (Some(ink), Some(page)) = (ink, page) else {
        return;
    };
    // Each step starts no nearer than the one before it landed, so pushing
    // secondary out cannot carry it past muted and invert the ramp.
    let mut reached = 0.0;
    for (key, step) in [
        ("content.secondary", Emphasis::Secondary),
        ("content.muted", Emphasis::Muted),
    ] {
        let (color, ratio) = step_clearing_floor(ink, page, step.ratio().max(reached));
        reached = ratio;
        colors.insert(key.to_string(), color.to_hex());
    }
}

/// The step `from` of the way from `ink` to `page`, pushed toward `page` until
/// it clears [`STEP_FLOOR`] against the ink it is a step of. Returns the colour
/// and the ratio it was found at.
///
/// A forward scan rather than a solve, because it wants the *first* ratio that
/// clears: contrast against the base rises with the distance travelled, but it
/// rises through sRGB's transfer curve and OKLab's chroma path, and a bisection
/// would trust a monotonicity nothing here guarantees.
///
/// Travel stops at the ground. A theme whose ink and page are the same colour
/// has no step to take, and the ground is the honest answer — nothing past it
/// is a step of the ink any more.
fn step_clearing_floor(ink: Rgb, page: Rgb, from: f32) -> (Rgb, f32) {
    // Finer than 8-bit sRGB can resolve on the shortest ramp in the corpus, so
    // the scan never steps over the first colour that clears.
    const PROBE: f32 = 0.005;
    let mut ratio = from.clamp(0.0, 1.0);
    loop {
        let color = tonal(ink, page, ratio);
        if wcag_contrast(color, ink) >= STEP_FLOOR || ratio >= 1.0 {
            return (color, ratio);
        }
        ratio = (ratio + PROBE).min(1.0);
    }
}

/// Scan directories for `.toml` theme files and return metadata for each.
///
/// Directories are checked in order; later entries override earlier ones by ID.
/// Each entry in `dirs` is `(path, is_custom)`.
pub fn list_themes_from_dirs(dirs: &[(PathBuf, bool)]) -> Vec<ThemeMeta> {
    let mut seen: HashMap<String, ThemeMeta> = HashMap::new();

    for (dir, is_custom) in dirs {
        let Ok(entries) = std::fs::read_dir(dir) else {
            continue;
        };

        for entry in entries {
            let Ok(entry) = entry else {
                continue;
            };
            let path = entry.path();
            if path.extension().and_then(|e| e.to_str()) != Some("toml") {
                continue;
            }

            let id = path
                .file_stem()
                .and_then(|s| s.to_str())
                .unwrap_or_default()
                .to_string();

            let Ok(content) = std::fs::read_to_string(&path) else {
                continue;
            };
            let table: toml::Table = match content.parse() {
                Ok(t) => t,
                Err(_) => continue,
            };

            seen.insert(id.clone(), parse_meta(&id, &table, *is_custom));
        }
    }

    let mut themes: Vec<ThemeMeta> = seen.into_values().collect();
    themes.sort_by(|a, b| a.name.cmp(&b.name));
    themes
}

/// Parse a complete theme (metadata + colors) from raw TOML content, with no
/// filesystem access. For callers that embed themes at compile time.
pub fn parse_theme_str(id: &str, content: &str, is_custom: bool) -> Result<ThemeColors, String> {
    validate_theme_id(id)?;
    let table: toml::Table = content
        .parse()
        .map_err(|e| format!("Failed to parse theme '{id}': {e}"))?;
    let meta = parse_meta(id, &table, is_custom);
    let colors = extract_colors(&table);
    Ok(ThemeColors { meta, colors })
}

/// Load a complete theme (metadata + colors) by ID from the given directories.
pub fn load_theme(dirs: &[(PathBuf, bool)], id: &str) -> Result<ThemeColors, String> {
    validate_theme_id(id)?;

    let (path, is_custom) =
        find_theme_path(dirs, id).ok_or_else(|| format!("Theme '{id}' not found"))?;

    let content = std::fs::read_to_string(&path)
        .map_err(|e| format!("Failed to read {}: {}", path.display(), e))?;

    let table: toml::Table = content
        .parse()
        .map_err(|e| format!("Failed to parse {}: {}", path.display(), e))?;

    let meta = parse_meta(id, &table, is_custom);
    let colors = extract_colors(&table);

    Ok(ThemeColors { meta, colors })
}

/// Load a theme and resolve it to the full intent token set in one step.
pub fn load_semantic(dirs: &[(PathBuf, bool)], id: &str) -> Result<SemanticTokens, String> {
    Ok(resolve(&load_theme(dirs, id)?))
}

/// Import a theme TOML file into the custom themes directory.
///
/// Validates that the file is parseable TOML with at least one intent color
/// section, then copies it to `custom_dir/{id}.toml`. Returns the theme metadata.
pub fn import_theme(source_path: &Path, custom_dir: &Path) -> Result<ThemeMeta, String> {
    let content = std::fs::read_to_string(source_path)
        .map_err(|e| format!("Failed to read {}: {}", source_path.display(), e))?;

    let table: toml::Table = content.parse().map_err(|e| format!("Invalid TOML: {e}"))?;

    let has_colors = COLOR_SECTIONS
        .iter()
        .any(|s| table.get(*s).and_then(|v| v.as_table()).is_some());
    if !has_colors {
        return Err(format!(
            "Theme file must have at least one color section ({})",
            COLOR_SECTIONS.join(", ")
        ));
    }

    let id = source_path
        .file_stem()
        .and_then(|s| s.to_str())
        .ok_or("Invalid file name")?
        .to_string();
    validate_theme_id(&id)?;

    std::fs::create_dir_all(custom_dir)
        .map_err(|e| format!("Failed to create {}: {}", custom_dir.display(), e))?;

    let dest = custom_dir.join(format!("{id}.toml"));
    std::fs::copy(source_path, &dest).map_err(|e| format!("Failed to copy theme: {e}"))?;

    Ok(parse_meta(&id, &table, true))
}

/// Delete a custom theme by ID.
///
/// Only operates on `custom_dir` — bundled themes are not deletable through
/// this entry point.
pub fn delete_theme(custom_dir: &Path, id: &str) -> Result<(), String> {
    validate_theme_id(id)?;

    let path = custom_dir.join(format!("{id}.toml"));
    if !path.is_file() {
        return Err(format!("Custom theme '{id}' not found"));
    }

    std::fs::remove_file(&path).map_err(|e| format!("Failed to delete {}: {}", path.display(), e))
}

/// A four-color preview for theme thumbnails: the representative swatch from
/// each of the principal roles.
#[derive(Debug, Clone, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct ThemePreview {
    pub meta: ThemeMeta,
    /// Page background (`surface.page`).
    pub background: Option<String>,
    /// Body text (`content.primary`).
    pub foreground: Option<String>,
    /// Brand/interactive color (`action.primary`).
    pub accent: Option<String>,
    /// Divider/outline color (`line.border`).
    pub border: Option<String>,
}

fn color_at(table: &toml::Table, section: &str, key: &str) -> Option<String> {
    table
        .get(section)
        .and_then(|s| s.as_table())
        .and_then(|s| s.get(key))
        .and_then(|v| v.as_str())
        .map(std::string::ToString::to_string)
}

/// Load just the preview swatches for a theme — for UI thumbnails.
pub fn load_theme_preview(dirs: &[(PathBuf, bool)], id: &str) -> Result<ThemePreview, String> {
    validate_theme_id(id)?;

    let (path, is_custom) =
        find_theme_path(dirs, id).ok_or_else(|| format!("Theme '{id}' not found"))?;

    let content = std::fs::read_to_string(&path)
        .map_err(|e| format!("Failed to read {}: {}", path.display(), e))?;

    let table: toml::Table = content
        .parse()
        .map_err(|e| format!("Failed to parse {}: {}", path.display(), e))?;

    Ok(ThemePreview {
        meta: parse_meta(id, &table, is_custom),
        background: color_at(&table, "surface", "page"),
        foreground: color_at(&table, "content", "primary"),
        accent: color_at(&table, "action", "primary"),
        border: color_at(&table, "line", "border"),
    })
}

/// Export a theme to a user-chosen path.
pub fn export_theme(dirs: &[(PathBuf, bool)], id: &str, dest_path: &Path) -> Result<(), String> {
    validate_theme_id(id)?;

    let (source, _) = find_theme_path(dirs, id).ok_or_else(|| format!("Theme '{id}' not found"))?;

    std::fs::copy(&source, dest_path).map_err(|e| format!("Failed to export theme: {e}"))?;

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::fixture::nord_toml;
    use crate::{bundled_themes_dir, embedded_themes};
    use std::fs;

    // ---- id validation ----

    #[test]
    fn validate_theme_id_alphanumeric() {
        assert!(validate_theme_id("darkmode").is_ok());
        assert!(validate_theme_id("Theme123").is_ok());
    }

    #[test]
    fn validate_theme_id_hyphens_underscores() {
        assert!(validate_theme_id("dark-mode").is_ok());
        assert!(validate_theme_id("my_theme_v2").is_ok());
    }

    #[test]
    fn validate_theme_id_rejects_path_traversal() {
        assert!(validate_theme_id("../etc/passwd").is_err());
        assert!(validate_theme_id("foo/bar").is_err());
        assert!(validate_theme_id("theme.toml").is_err());
    }

    // ---- meta ----

    #[test]
    fn parse_meta_with_name_and_variant() {
        let table: toml::Table = "[meta]\nname = \"Nord\"\nvariant = \"light\"\n"
            .parse()
            .unwrap();
        let meta = parse_meta("nord", &table, false);
        assert_eq!(meta.id, "nord");
        assert_eq!(meta.name, "Nord");
        assert_eq!(meta.variant, "light");
        assert!(!meta.is_custom);
    }

    #[test]
    fn parse_meta_defaults_to_id_and_dark() {
        let table: toml::Table = "".parse().unwrap();
        let meta = parse_meta("fallback", &table, true);
        assert_eq!(meta.name, "fallback");
        assert_eq!(meta.variant, "dark");
        assert!(meta.is_custom);
    }

    #[test]
    fn extract_colors_reads_intent_sections() {
        let table: toml::Table = nord_toml().parse().unwrap();
        let colors = extract_colors(&table);
        assert_eq!(colors.get("surface.page").unwrap(), "#2e3440");
        assert_eq!(colors.get("content.primary").unwrap(), "#d8dee9");
        assert_eq!(colors.get("action.primary").unwrap(), "#81a1c1");
        assert_eq!(colors.get("status.danger").unwrap(), "#bf616a");
        assert_eq!(colors.get("line.border").unwrap(), "#4c566a");
        assert_eq!(colors.get("category.five").unwrap(), "#b48ead");
        assert_eq!(colors.len(), 19);
    }

    #[test]
    fn every_shipped_theme_ramps_one_way() {
        // The property authoring the steps separately could not hold: three
        // themes had shipped a secondary lighter than their own primary, so a
        // renderer reading the emphasis order got the reverse of it.
        for (id, toml) in embedded_themes() {
            let theme = parse_theme_str(id, toml, false).unwrap();
            let t = resolve(&theme);
            let page = Rgb::from_hex(t.hex("surface-page").unwrap()).unwrap();
            let steps = ["content", "content-secondary", "content-muted"]
                .map(|k| wcag_contrast(Rgb::from_hex(t.hex(k).unwrap()).unwrap(), page));
            assert!(
                steps[0] > steps[1] && steps[1] > steps[2],
                "{id}: emphasis does not fall monotonically: {steps:?}"
            );
        }
    }

    #[test]
    fn every_shipped_theme_takes_a_visible_first_step() {
        // The property that was missing when 2.6.0 derived these, and the
        // reason a pure-black ink shipped a secondary 3/255 away from it: the
        // ramp falling monotonically says nothing about how far it falls, and
        // a step nobody can see is not a step.
        for (id, toml) in embedded_themes() {
            let theme = parse_theme_str(id, toml, false).unwrap();
            let t = resolve(&theme);
            let ink = Rgb::from_hex(t.hex("content").unwrap()).unwrap();
            let secondary = Rgb::from_hex(t.hex("content-secondary").unwrap()).unwrap();
            let step = wcag_contrast(ink, secondary);
            assert!(
                step >= STEP_FLOOR,
                "{id}: secondary is {step:.2} from its ink, under the {STEP_FLOOR} floor"
            );
        }
    }

    #[test]
    fn an_authored_emphasis_step_does_not_survive_loading() {
        // `nord_toml` still authors both, because a user's theme file might and
        // the answer has to be the same one.
        let theme = parse_theme_str("nord", nord_toml(), false).unwrap();
        assert_ne!(theme.colors.get("content.muted").unwrap(), "#616e88");
        assert_ne!(theme.colors.get("content.secondary").unwrap(), "#e5e9f0");
    }

    #[test]
    fn a_theme_with_no_page_keeps_what_it_authored() {
        // Skip-missing: there is nothing to read the step against, so the step
        // is not taken and a half-written theme does not lose a colour.
        let mut colors = HashMap::new();
        colors.insert("content.primary".to_string(), "#d8dee9".to_string());
        colors.insert("content.muted".to_string(), "#616e88".to_string());
        derive_tonal_steps(&mut colors);
        assert_eq!(colors.get("content.muted").unwrap(), "#616e88");
    }

    // ---- loading / fs ----

    #[test]
    fn load_and_resolve_round_trip() {
        let dir = tempfile::tempdir().unwrap();
        fs::write(dir.path().join("nord.toml"), nord_toml()).unwrap();
        let dirs = vec![(dir.path().to_path_buf(), false)];
        let t = load_semantic(&dirs, "nord").unwrap();
        assert_eq!(t.meta.name, "Nord");
        assert_eq!(t.hex("action"), Some("#81a1c1"));
    }

    #[test]
    fn load_theme_rejects_invalid_id() {
        assert!(load_theme(&[], "../evil").is_err());
    }

    #[test]
    fn list_themes_from_dirs_finds_toml_files() {
        let dir = tempfile::tempdir().unwrap();
        fs::write(dir.path().join("t.toml"), "[meta]\nname = \"T\"\n").unwrap();
        fs::write(dir.path().join("x.txt"), "ignored").unwrap();
        let dirs = vec![(dir.path().to_path_buf(), false)];
        let themes = list_themes_from_dirs(&dirs);
        assert_eq!(themes.len(), 1);
        assert_eq!(themes[0].id, "t");
    }

    #[test]
    fn import_theme_valid_and_rejects_empty() {
        let src_dir = tempfile::tempdir().unwrap();
        let custom_dir = tempfile::tempdir().unwrap();

        let good = src_dir.path().join("my-theme.toml");
        fs::write(&good, "[surface]\npage = \"#1a1b26\"\n").unwrap();
        let meta = import_theme(&good, custom_dir.path()).unwrap();
        assert_eq!(meta.id, "my-theme");
        assert!(custom_dir.path().join("my-theme.toml").exists());

        let empty = src_dir.path().join("empty.toml");
        fs::write(&empty, "[meta]\nname = \"E\"\n").unwrap();
        assert!(import_theme(&empty, custom_dir.path()).is_err());
    }

    #[test]
    fn import_theme_rejects_invalid_toml() {
        let src_dir = tempfile::tempdir().unwrap();
        let custom_dir = tempfile::tempdir().unwrap();
        let src = src_dir.path().join("bad.toml");
        fs::write(&src, "this is not [valid toml [[[").unwrap();
        assert!(import_theme(&src, custom_dir.path()).is_err());
    }

    #[test]
    fn delete_theme_removes_and_guards() {
        let custom = tempfile::tempdir().unwrap();
        let path = custom.path().join("doomed.toml");
        fs::write(&path, "[surface]\npage = \"#000\"\n").unwrap();
        delete_theme(custom.path(), "doomed").unwrap();
        assert!(!path.exists());
        assert!(delete_theme(custom.path(), "../etc/passwd").is_err());
        assert!(delete_theme(custom.path(), "ghost").is_err());
    }

    #[test]
    fn export_theme_copies_file() {
        let src_dir = tempfile::tempdir().unwrap();
        let dest_dir = tempfile::tempdir().unwrap();
        let content = "[meta]\nname = \"E\"\n[surface]\npage = \"#ffffff\"\n";
        fs::write(src_dir.path().join("e.toml"), content).unwrap();
        let dirs = vec![(src_dir.path().to_path_buf(), false)];
        let dest = dest_dir.path().join("out.toml");
        export_theme(&dirs, "e", &dest).unwrap();
        assert_eq!(fs::read_to_string(&dest).unwrap(), content);
        assert!(export_theme(&dirs, "missing", &dest).is_err());
    }

    #[test]
    fn load_theme_preview_returns_role_swatches() {
        let dir = tempfile::tempdir().unwrap();
        fs::write(dir.path().join("nord.toml"), nord_toml()).unwrap();
        let dirs = vec![(dir.path().to_path_buf(), false)];
        let p = load_theme_preview(&dirs, "nord").unwrap();
        assert_eq!(p.background.as_deref(), Some("#2e3440")); // surface.page
        assert_eq!(p.foreground.as_deref(), Some("#d8dee9")); // content.primary
        assert_eq!(p.accent.as_deref(), Some("#81a1c1")); // action.primary
        assert_eq!(p.border.as_deref(), Some("#4c566a")); // line.border
    }

    #[test]
    fn every_shipped_theme_loads() {
        // Guards the data, not just the loader: a malformed or truncated
        // .toml in themes/ is a shipping bug, and it should fail here rather
        // than at a user's first launch.
        let dir = bundled_themes_dir().unwrap();
        let dirs = vec![(dir.clone(), false)];
        let themes = list_themes_from_dirs(&dirs);
        assert!(
            themes.len() >= 30,
            "expected the full theme set, got {}",
            themes.len()
        );
        for meta in &themes {
            load_theme(&dirs, &meta.id)
                .unwrap_or_else(|e| panic!("shipped theme `{}` failed to load: {e}", meta.id));
        }
    }
}