//
//  KBSuggestionEngine.m
//  CustomKeyboard
//

#import "KBSuggestionEngine.h"
#import "KBConfig.h"

@interface KBSuggestionEngine ()
@property (nonatomic, copy) NSArray<NSString *> *words;
@property (nonatomic, strong) NSMutableDictionary<NSString *, NSNumber *> *selectionCounts;
@property (nonatomic, strong) NSSet<NSString *> *priorityWords;
@end

@implementation KBSuggestionEngine

+ (instancetype)shared {
    static KBSuggestionEngine *engine;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        engine = [[KBSuggestionEngine alloc] init];
    });
    return engine;
}

- (instancetype)init {
    if (self = [super init]) {
        _selectionCounts = [NSMutableDictionary dictionary];
        NSArray<NSString *> *defaults = [self.class kb_defaultWords];
        _priorityWords = [NSSet setWithArray:defaults];
        _words = [self kb_loadWords];
    }
    return self;
}

- (NSArray<NSString *> *)suggestionsForPrefix:(NSString *)prefix limit:(NSUInteger)limit {
    if (prefix.length == 0 || limit == 0) { return @[]; }
    NSString *lower = prefix.lowercaseString;
    NSMutableArray<NSString *> *matches = [NSMutableArray array];

    for (NSString *word in self.words) {
        if ([word hasPrefix:lower]) {
            [matches addObject:word];
            if (matches.count >= limit * 3) {
                // Avoid scanning too many matches for long lists.
                break;
            }
        }
    }

    if (matches.count == 0) { return @[]; }

    [matches sortUsingComparator:^NSComparisonResult(NSString *a, NSString *b) {
        NSInteger ca = self.selectionCounts[a].integerValue;
        NSInteger cb = self.selectionCounts[b].integerValue;
        if (ca != cb) {
            return (cb > ca) ? NSOrderedAscending : NSOrderedDescending;
        }
        BOOL pa = [self.priorityWords containsObject:a];
        BOOL pb = [self.priorityWords containsObject:b];
        if (pa != pb) {
            return pa ? NSOrderedAscending : NSOrderedDescending;
        }
        return [a compare:b];
    }];

    if (matches.count > limit) {
        return [matches subarrayWithRange:NSMakeRange(0, limit)];
    }
    return matches.copy;
}

- (void)recordSelection:(NSString *)word {
    if (word.length == 0) { return; }
    NSString *key = word.lowercaseString;
    NSInteger count = self.selectionCounts[key].integerValue + 1;
    self.selectionCounts[key] = @(count);
}

#pragma mark - Defaults

- (NSArray<NSString *> *)kb_loadWords {
    NSMutableOrderedSet<NSString *> *set = [[NSMutableOrderedSet alloc] init];
    [set addObjectsFromArray:[self.class kb_defaultWords]];

    NSArray<NSString *> *paths = [self kb_wordListPaths];
    for (NSString *path in paths) {
        if (path.length == 0) { continue; }
        NSString *content = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];
        if (content.length == 0) { continue; }
        NSArray<NSString *> *lines = [content componentsSeparatedByCharactersInSet:[NSCharacterSet newlineCharacterSet]];
        for (NSString *line in lines) {
            NSString *word = [self kb_sanitizedWordFromLine:line];
            if (word.length == 0) { continue; }
            [set addObject:word];
        }
    }

    NSArray<NSString *> *result = set.array ?: @[];
    return result;
}

- (NSArray<NSString *> *)kb_wordListPaths {
    NSMutableArray<NSString *> *paths = [NSMutableArray array];
    // 1) App Group override (allows server-downloaded large list).
    NSURL *containerURL = [[NSFileManager defaultManager] containerURLForSecurityApplicationGroupIdentifier:AppGroup];
    if (containerURL.path.length > 0) {
        NSString *groupPath = [[containerURL path] stringByAppendingPathComponent:@"kb_words.txt"];
        [paths addObject:groupPath];
    }
    // 2) Bundle fallback.
    NSString *bundlePath = [[NSBundle mainBundle] pathForResource:@"kb_words" ofType:@"txt"];
    if (bundlePath.length > 0) {
        [paths addObject:bundlePath];
    }
    return paths;
}

- (NSString *)kb_sanitizedWordFromLine:(NSString *)line {
    NSString *trimmed = [[line stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] lowercaseString];
    if (trimmed.length == 0) { return @""; }
    static NSCharacterSet *letters = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        letters = [NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyz"];
    });
    for (NSUInteger i = 0; i < trimmed.length; i++) {
        if (![letters characterIsMember:[trimmed characterAtIndex:i]]) {
            return @"";
        }
    }
    return trimmed;
}

+ (NSArray<NSString *> *)kb_defaultWords {
    return @[
        @"a", @"an", @"and", @"are", @"as", @"at",
        @"app", @"ap", @"apple", @"apply", @"april", @"application",
        @"about", @"above", @"after", @"again", @"against", @"all",
        @"am", @"among", @"amount", @"any", @"around",
        @"be", @"because", @"been", @"before", @"being", @"below",
        @"best", @"between", @"both", @"but", @"by",
        @"can", @"could", @"come", @"common", @"case",
        @"do", @"does", @"down", @"day",
        @"each", @"early", @"end", @"even", @"every",
        @"for", @"from", @"first", @"found", @"free",
        @"get", @"good", @"great", @"go",
        @"have", @"has", @"had", @"help", @"how",
        @"in", @"is", @"it", @"if", @"into",
        @"just", @"keep", @"kind", @"know",
        @"like", @"look", @"long", @"last",
        @"make", @"more", @"most", @"my",
        @"new", @"no", @"not", @"now",
        @"of", @"on", @"one", @"or", @"other", @"our", @"out",
        @"people", @"place", @"please",
        @"quick", @"quite",
        @"right", @"read", @"real",
        @"see", @"say", @"some", @"such", @"so",
        @"the", @"to", @"this", @"that", @"them", @"then", @"there", @"they", @"these", @"time",
        @"use", @"up", @"under",
        @"very",
        @"we", @"with", @"what", @"when", @"where", @"who", @"why", @"will", @"would",
        @"you", @"your"
    ];
}

@end