use std::collections::BTreeMap;

use crank_schema::{Schema, SchemaKind};
use serde_json::Value;

pub fn any_object(description: Option<String>) -> Schema {
    Schema {
        kind: SchemaKind::Object,
        description,
        required: true,
        nullable: false,
        default_value: None,
        fields: BTreeMap::new(),
        items: None,
        enum_values: Vec::new(),
        variants: Vec::new(),
    }
}

pub fn field_count(schema: &Schema) -> usize {
    match schema.kind {
        SchemaKind::Object => schema.fields.len(),
        _ => 0,
    }
}

pub fn schema_from_openapi(
    value: Option<&Value>,
    required: bool,
    description: Option<String>,
) -> Schema {
    let Some(value) = value else {
        return primitive(SchemaKind::String, required, description);
    };
    // Only v3 NormalizedIR emits the private marker. Pending legacy-v1 jobs
    // retain their historical first-branch behavior, while modern oneOf/anyOf
    // is projected losslessly through crank-schema's existing Oneof shape.
    if value
        .get("x-crank-lossless-composition")
        .and_then(Value::as_bool)
        == Some(true)
        && let Some(items) = value
            .get("oneOf")
            .or_else(|| value.get("anyOf"))
            .and_then(Value::as_array)
    {
        return Schema {
            kind: SchemaKind::Oneof,
            description: description.or_else(|| text(value, "description")),
            required,
            nullable: nullable(value),
            default_value: value.get("default").cloned(),
            fields: BTreeMap::new(),
            items: None,
            enum_values: Vec::new(),
            variants: items
                .iter()
                .map(|item| schema_from_openapi(Some(item), true, None))
                .collect(),
        };
    }
    let resolved = collapse_composition(value);

    if let Some(values) = resolved.get("enum").and_then(Value::as_array) {
        let enum_values = values
            .iter()
            .filter_map(Value::as_str)
            .map(ToOwned::to_owned)
            .collect::<Vec<_>>();
        if !enum_values.is_empty() {
            return Schema {
                kind: SchemaKind::Enum,
                description: description.or_else(|| text(&resolved, "description")),
                required,
                nullable: nullable(&resolved),
                default_value: resolved.get("default").cloned(),
                fields: BTreeMap::new(),
                items: None,
                enum_values,
                variants: Vec::new(),
            };
        }
    }

    match type_name(&resolved).unwrap_or("object") {
        "object" => object_schema(&resolved, required, description),
        "array" => Schema {
            kind: SchemaKind::Array,
            description: description.or_else(|| text(&resolved, "description")),
            required,
            nullable: nullable(&resolved),
            default_value: resolved.get("default").cloned(),
            fields: BTreeMap::new(),
            items: Some(Box::new(schema_from_openapi(
                resolved.get("items"),
                true,
                None,
            ))),
            enum_values: Vec::new(),
            variants: Vec::new(),
        },
        "integer" => primitive(
            SchemaKind::Integer,
            required,
            description.or_else(|| text(&resolved, "description")),
        ),
        "number" => primitive(
            SchemaKind::Number,
            required,
            description.or_else(|| text(&resolved, "description")),
        ),
        "boolean" => primitive(
            SchemaKind::Boolean,
            required,
            description.or_else(|| text(&resolved, "description")),
        ),
        "null" => primitive(
            SchemaKind::Null,
            required,
            description.or_else(|| text(&resolved, "description")),
        ),
        _ => primitive(
            SchemaKind::String,
            required,
            description.or_else(|| text(&resolved, "description")),
        ),
    }
}

fn collapse_composition(value: &Value) -> Value {
    for key in ["allOf", "oneOf", "anyOf"] {
        if let Some(items) = value.get(key).and_then(Value::as_array)
            && let Some(first) = items.first()
        {
            return first.clone();
        }
    }
    value.clone()
}

pub fn object_with_fields(description: Option<String>, fields: BTreeMap<String, Schema>) -> Schema {
    Schema {
        kind: SchemaKind::Object,
        description,
        required: true,
        nullable: false,
        default_value: None,
        fields,
        items: None,
        enum_values: Vec::new(),
        variants: Vec::new(),
    }
}

fn object_schema(value: &Value, required: bool, description: Option<String>) -> Schema {
    let required_fields = value
        .get("required")
        .and_then(Value::as_array)
        .map(|items| {
            items
                .iter()
                .filter_map(Value::as_str)
                .collect::<std::collections::BTreeSet<_>>()
        })
        .unwrap_or_default();
    let mut fields = BTreeMap::new();

    if let Some(properties) = value.get("properties").and_then(Value::as_object) {
        for (name, schema) in properties {
            fields.insert(
                name.clone(),
                schema_from_openapi(
                    Some(schema),
                    required_fields.contains(name.as_str()),
                    text(schema, "description"),
                ),
            );
        }
    }

    Schema {
        kind: SchemaKind::Object,
        description: description.or_else(|| text(value, "description")),
        required,
        nullable: nullable(value),
        default_value: value.get("default").cloned(),
        fields,
        items: None,
        enum_values: Vec::new(),
        variants: Vec::new(),
    }
}

fn primitive(kind: SchemaKind, required: bool, description: Option<String>) -> Schema {
    Schema {
        kind,
        description,
        required,
        nullable: false,
        default_value: None,
        fields: BTreeMap::new(),
        items: None,
        enum_values: Vec::new(),
        variants: Vec::new(),
    }
}

fn type_name(value: &Value) -> Option<&str> {
    match value.get("type") {
        Some(Value::String(value)) => Some(value.as_str()),
        Some(Value::Array(values)) => values.iter().find_map(Value::as_str),
        _ if value.get("properties").is_some() => Some("object"),
        _ if value.get("items").is_some() => Some("array"),
        _ => None,
    }
}

fn nullable(value: &Value) -> bool {
    value
        .get("nullable")
        .and_then(Value::as_bool)
        .unwrap_or(false)
}

fn text(value: &Value, key: &str) -> Option<String> {
    value
        .get(key)
        .and_then(Value::as_str)
        .map(ToOwned::to_owned)
}