// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license that can be found in the LICENSE file.

module font

import os

// Variant enumerates the different variants a font can have.
pub enum Variant {
    normal = 0
    bold
    mono
    italic
}

@[if debug_font ?]
fn debug_font_println(s string) {
    println(s)
}

fn is_readable_font_file(font_path string) bool {
    if font_path == '' {
        return false
    }
    return !font_path.to_lower().ends_with('.ttc') && os.is_file(font_path)
        && os.is_readable(font_path)
}

fn use_font_if_readable(font_path string) string {
    if is_readable_font_file(font_path) {
        debug_font_println('Using font "${font_path}"')
        return font_path
    }
    return ''
}

fn find_first_font_in_paths(font_paths []string) string {
    for font_path in font_paths {
        if is_readable_font_file(font_path) {
            return font_path.clone()
        }
    }
    return ''
}

fn find_first_font_in_dirs(font_dirs []string) string {
    for font_dir in font_dirs {
        if !os.is_dir(font_dir) {
            continue
        }
        mut font_paths := os.walk_ext(font_dir, '.ttf')
        font_paths.sort()
        font_path := find_first_font_in_paths(font_paths)
        if font_path != '' {
            return font_path
        }
    }
    return ''
}

fn default_user_font_dirs() []string {
    mut font_dirs := []string{}
    if config_dir := os.config_dir() {
        font_dirs << os.join_path(config_dir, 'v', 'fonts')
    }
    return font_dirs
}

fn bundled_font_dirs() []string {
    return [os.join_path(@VEXEROOT, 'examples', 'assets', 'fonts')]
}

fn find_fc_match_font(output string) string {
    return find_first_font_in_paths(output.split('\n'))
}

// default returns an absolute path to a readable default font.
// Search order:
// 1. The env variable `VUI_FONT`.
// 2. A user-provided fallback font under `${os.config_dir()}/v/fonts`.
// 3. Platform defaults and `fc-match`.
// 4. Bundled fonts under `@VEXEROOT/examples/assets/fonts`.
// NOTE that, in some cases, the function calls out to external OS programs
// so running this in a hot loop is not advised.
@[manualfree]
pub fn default() string {
    env_font := os.getenv('VUI_FONT')
    if env_font != '' && os.is_file(env_font) && os.is_readable(env_font) {
        debug_font_println('Using font "${env_font}"')
        return env_font
    }
    unsafe { env_font.free() }
    user_font_path := find_first_font_in_dirs(default_user_font_dirs())
    if user_font_path != '' {
        debug_font_println('Using font "${user_font_path}"')
        return user_font_path
    }
    $if windows {
        fonts := ['C:\\Windows\\Fonts\\segoeui.ttf', 'C:\\Windows\\Fonts\\arial.ttf']
        for system_font in fonts {
            existing_font := use_font_if_readable(system_font)
            if existing_font != '' {
                return existing_font
            }
        }
    }
    $if macos {
        fonts := ['/System/Library/Fonts/SFNS.ttf', '/System/Library/Fonts/SFNSText.ttf',
            '/Library/Fonts/Arial.ttf']
        for system_font in fonts {
            existing_font := use_font_if_readable(system_font)
            if existing_font != '' {
                return existing_font
            }
        }
        unsafe { fonts.free() }
    }
    $if android {
        xml_files := ['/system/etc/system_fonts.xml', '/system/etc/fonts.xml',
            '/etc/system_fonts.xml', '/etc/fonts.xml', '/data/fonts/fonts.xml',
            '/etc/fallback_fonts.xml']
        font_locations := ['/system/fonts', '/data/fonts']
        for xml_file in xml_files {
            if os.is_file(xml_file) && os.is_readable(xml_file) {
                xml := os.read_file(xml_file) or { continue }
                lines := xml.split('\n')
                mut candidate_font := ''
                for line in lines {
                    if line.contains('<font') {
                        tmp1 := line.all_after('>')
                        tmp2 := tmp1.all_before('<')
                        tmp3 := tmp2.trim(' \n\t\r')
                        mut_assign(candidate_font, tmp3)
                        if candidate_font.contains('.ttf') {
                            for location in font_locations {
                                candidate_path := os.join_path_single(location, candidate_font)
                                existing_font := use_font_if_readable(candidate_path)
                                if existing_font != '' {
                                    return existing_font
                                }
                                unsafe { candidate_path.free() }
                            }
                        }
                        unsafe { tmp3.free() }
                        unsafe { tmp2.free() }
                        unsafe { tmp1.free() }
                    }
                }
                unsafe { candidate_font.free() }
                unsafe { lines.free() }
                unsafe { xml.free() }
            }
        }
        unsafe { font_locations.free() }
        unsafe { xml_files.free() }
    }
    mut fm := os.execute("fc-match --format='%{file}\n' -s")
    if fm.exit_code == 0 {
        fc_match_font_path := find_fc_match_font(fm.output)
        if fc_match_font_path != '' {
            unsafe { fm.free() }
            debug_font_println('Using font "${fc_match_font_path}"')
            return fc_match_font_path
        }
    } else {
        debug_font_println('fc-match failed to fetch system font')
    }
    unsafe { fm.free() }
    bundled_font_path := find_first_font_in_dirs(bundled_font_dirs())
    if bundled_font_path != '' {
        debug_font_println('Using font "${bundled_font_path}"')
        return bundled_font_path
    }
    panic('failed to init the font')
}

// get_path_variant returns the `font_path` file name replaced with the
// file name of the font's `variant` version if it exists.
@[manualfree]
pub fn get_path_variant(font_path string, variant Variant) string {
    // TODO: find some way to make this shorter and more eye-pleasant
    // NotoSans, LiberationSans, DejaVuSans, Arial and SFNS should work
    mut file := os.file_name(font_path)
    defer { unsafe { file.free() } }

    mut fpath := font_path.replace(file, '')
    defer { unsafe { fpath.free() } }

    mut_replace(file, '.ttf', '')

    flower := file.to_lower()
    defer { unsafe { flower.free() } }

    match variant {
        .normal {}
        .bold {
            if fpath.ends_with('-Regular') {
                mut_replace(file, '-Regular', '-Bold')
            } else if file.starts_with('DejaVuSans') {
                mut_plus(file, '-Bold')
            } else if flower.starts_with('arial') {
                mut_plus(file, 'bd')
            } else {
                mut_plus(file, '-bold')
            }
            $if macos {
                if os.exists('SFNS-bold') {
                    mut_assign(file, 'SFNS-bold')
                }
            }
        }
        .italic {
            if file.ends_with('-Regular') {
                mut_replace(file, '-Regular', '-Italic')
            } else if file.starts_with('DejaVuSans') {
                mut_plus(file, '-Oblique')
            } else if flower.starts_with('arial') {
                mut_plus(file, 'i')
            } else {
                mut_plus(file, 'Italic')
            }
        }
        .mono {
            if !file.ends_with('Mono-Regular') && file.ends_with('-Regular') {
                mut_replace(file, '-Regular', 'Mono-Regular')
            } else if flower.starts_with('arial') {
                // Arial has no mono variant
            } else {
                mut_plus(file, 'Mono')
            }
        }
    }

    res := '${fpath}${file}.ttf'
    return res
}

@[manualfree]
fn mut_replace(s &string, find string, replacement string) {
    new := (*s).replace(find, replacement)
    unsafe { s.free() }
    unsafe {
        *s = new
    }
}

@[manualfree]
fn mut_plus(s &string, tail string) {
    new := (*s) + tail
    unsafe { s.free() }
    unsafe {
        *s = new
    }
}

@[manualfree]
fn mut_assign(s &string, value string) {
    unsafe { s.free() }
    unsafe {
        *s = value.clone()
    }
}